Integumentary System

Abstract

Skin is a complex organ, consisting of several layers, each containing different kinds of cells performing different functions, including defense mechanisms against pathogens, chemicals, UV light, and mechanical injury, hydration, temperature regulation, sebum production, skin blood flow and barrier function. Skin is regulated by the central clock, while skin cells also harbor their own molecular circuitry, with each cell containing a biochemical oscillator consisting of interlocked transcription–translation feedback loops. After a brief overview of skin structure and organization, illustrative examples of 24-hour variations in some functions of skin are presented. The involvement of the circadian clock in several cells playing key roles in skin and affecting the expression of distinct gene sets and physiological functions is then reviewed. The implication of the circadian clock machinery present in different skin cells is further discussed in relation to various skin diseases, ranging from skin cancer to skin infections, inflammatory skin diseases, and wound healing. To conclude, some thoughts on strategies to maintain skin health and counteract disease conditions in the skin are offered, opening a vast field for future investigation.